MINNEAPOLIS -- Newly-discovered DNA evidence may prove that a man known as a Minnesota serial killer might be innocent and that the real killer is someone else.

Attorneys for Billy Glaze, 70, filed court documents late Tuesday asking that his conviction be thrown out and that he get a new trial in light of the DNA evidence.

Glaze is serving three life sentences for the murders of three American Indian women in Minneapolis in 1986 and 1987. Kathleen Bullman, Angeline Whitebird Sweet and Angela Green were raped, murdered and mutilated in similar ways, leading police to search for a serial killer.

Kathleen Bullman's body was found in July 1986 in the brush under a tree near a railroad warehouse at 10th and Holden in Minneapolis. Angeline Whitebird Sweet's body was found in the back of the American Indian Center at Franklin and Bloomington Avenues in April 1987. The third victim, Angela Green was discovered under the Park Avenue Railroad Bridge, the same month.

Glaze, a drifter with a long criminal record, soon emerged as the prime suspect. Authorities said he was known to make derogatory comments about American Indian women. At the 1989 trial, several inmates testified they heard Glaze admit to the murders. One man claimed he'd seen Glaze with one of the victims.

Glaze, who has always maintained his innocence, was convicted in 1989, though prosecutors at the time acknowledged there was little physical evidence tying him to the murders – only a footprint never confirmed to belong to Glaze.

"I did not murder nobody. I couldn't murder nobody. I don't have it in my heart to," Glaze told KARE 11 in a 1987 interview from a Dallas jail where he had been picked up on a probation violation.

Glaze had a long criminal record, including convictions for rape, drunk driving, Social Security fraud, disorderly conduct and counterfeiting. His high-profile murder trial was heavily covered by the media. At the time, prosecutors called it one of the most extensive investigations ever in Minneapolis, interviewing hundreds of witnesses throughout the country.

The Innocence Project had three labs run DNA tests on dozens of pieces of evidence from the three Minneapolis crime scenes that led to Glaze's conviction. It took years to get all of the results. But Glaze's attorneys say those results show there is no trace of DNA belonging to Glaze at any of the crime scenes, proving his innocence.

"In a case like this where not only is it a violent homicide but there's also a sexual assault involved, you would certainly expect to see some DNA from the perpetrator at the scene and we didn't find any DNA from Billy Glaze," said Innocence Project lawyer Olga Akselrod.

Instead, the group said tests showed the DNA profile of another man – a convicted rapist – at two of the three murder scenes. A full DNA profile of the man was found on a rape swab taken from victim Angela Green, according to the Innocence Project.

A second partial profile was located on a fresh cigarette butt collected as evidence from the Angeline Whitebird Sweet murder scene.

"You look at the evidence that they were able to present against Billy Glaze at the time of trial. It was the best they could come up with, with the tools they had available at the time," said Julie Jonas, an attorney with the Innocence Project of Minnesota.

"If they would have had what they have now against this person who really did the crimes, he would have been the one who was arrested. He would have been the one on trial," she added. "Billy Glaze would never have gone to prison for all those 27 years."

Innocence Project attorneys say in the 1980s, blood-typing was among the only tools law enforcement had to identify biological evidence. Today, DNA analysis can lead to a map of a person's genetic fingerprint.

According to the Innocence Project, the DNA profile belongs to a man who kidnapped and raped a different American Indian woman in 1989. She survived the attack and he served time for that assault.

They say police interviewed the man in 2012 when he was in jail for failing to register as a sex offender. He still lives in Minneapolis, and according to a transcript of the police interview, the man denied knowing or having sex with Green.

In addition to the DNA evidence, Innocence Project attorneys point to two other factors that may have compromised Glaze's trial: a key prosecution witness who testified he saw Glaze with one of the victims has now recanted his testimony; and, at the time of his trial, Glaze's defense attorneys were not told about important information they could have used to question the credibility of other witnesses.

"This case is about a man who has been in prison for 27 years for a horrible crime he did not commit," said Ed Magarian of Dorsey & Whitney, a Minneapolis law firm and partner on this case with Innocence Project.

The Hennepin County Attorney's office has not yet responded to the petition.